Predictable effects of storage time on δ 13C and δ 15N values of the ethanol-preserved nymphs of Epeorus vitreus (Walker, 1853) and Acentrella turbida (McDunnough, 1924) (Ephemeroptera) Aquatic Insects

Preserved samples of benthic macroinvertebrates may be useful for examining spatiotemporal changes in aquatic food webs. However, archived samples preserved in ethanol may have altered isotopic values because of the effects of ethanol on tissue composition. Two mayfly species, Epeorus vitreus (Walker, Citation1853) (Ephemeroptera: Heptageniidae) and Acentrella turbida (McDunnough, Citation1924) (Ephemeroptera: Baetidae) were collected from Wills Creek and the Savage River, Maryland, USA. We measured five replicates for whole body %carbon, %nitrogen, δ13C, and δ15N at Day 0 (fresh, not stored in ethanol) and then two weeks, one month, three months, six months, nine months, and 12 months following storage in 95% ethanol. Within one week, ethanol preservation typically caused δ13C values to increase by 0.5-1‰; whereas, changes in δ15N values were < 1‰ or absent. Changes in δ13C occurred coincident with declines in tissue C:N ratios and % C, likely due to leaching of lipids from tissues. These results indicate that long-term ethanol preservation is unlikely to bias δ15N values of archived stream invertebrates, supporting the use of preserved specimens in future studies of changing nitrogen dynamics through time. Furthermore, results do not support the use of C:N as an index of lipid-storage in ethanol-preserved macroinvertebrates. Grant no. NA18OAR4170070